Cholera continues to be a major public health problem in developing countries. During 2003 forty five countries officially reported to WHO 111,575 cases of cholera and 1,984 deaths. Unfortunately, there is still not an inexpensive and safe cholera vaccine affording long term protection in all age groups particularly in children under five years old. The live genetically attenuated cholera vaccine candidate Vibrio cholerae 638 adhere strongly to mucosal surfaces in vitro and in vivo and induces strong local and systemic immune responses and protection against cholera in animal models and humans without inducing significant side effects (reactogenicity). Tetanus continues to be a global health problem that accounts for 14% of vaccinepreventable deaths and 500,000 cases of neonatal tetanus per year. Cholera and tetanus share similar geographic distribution. In this project we will develop a novel cholera-tetanus vaccine that lyses in the gut to deliver a tetanus protective antigen rather than being shed to the environment. To achieve this goal we will manipulate the bacterial quorum sensing system so that the live vaccine strain will only sense its cell density in vivo (low iron or anaerobiosis) to express a phage lysis gene under the control of a cell density-dependent promoter. Programmed cell lysis in the gut will allow the massive delivery of immunogenic and protective tetanus C fragment (TCP) to mucosal inductive sites. The capacity of this new vaccine to lyse in the small intestine, deliver TCP and induce protective immunity to cholera and tetanus will be determined using the suckling mouse model, adult rabbits ileal loops and the adult germ-free mice model. The development of the above cholera-tetanus combination vaccine could significantly improve the cost-benefit ratio of a massive vaccination program in endemic areas. In addition, lysis of the vaccine strain in the gut will reduce shedding of live vaccine strain to the environment. The novelty of our approach consists in manipulating a bacterial quorum sensing pathway to alter the course of an infective process and to achieve programmed antigen delivery and lysis of the vaccine vector in the host.